A spinning machine generally comprises a drafting frame and a multiplicity of spinning stations, the drafting frame comprising a number of roller pairs through which the roving passes for drafting or drawing between the roller pairs which can be operated at successively higher peripheral speeds. The lower rollers of the roller pairs may be continuous, i.e. rollers that extend the full length of the drafting frame, while the upper rollers or pressing rollers may be mounted in the weighting or loading arm and can be specific to the particular spinning station. Twinned upper rollers are commonly also provided, i.e. each arm may press two upper rollers against one of the continuous lower rollers.
At each spinning station the roving or, where two or more rovings are supplied to a given station, the plurality of rovings thus supplied are twisted and wound up in a yarn body.
The condensing or compacting system for a roving or slubbing can be provided as described in German patent document DE 44 26 249 A1 or EP 0 635 590 A2. In the first case, the condensing device is in the form of a rotatable cylindrical roller which is provided along its periphery with a row of perforations. The perforations can be maintained under suction and the roller can be referred to as a suction roller. In the EP 0 635 590 A2 publication, the row of perforations is provided on an endless flexible belt and suction can be applied to these perforations as well.
The condensing or compaction operation applies a roving delivered by a drafting frame, has the advantage of drawing the roving together so that when it enters the twisting zone it is substantially more compact than when, as sliver or slubbing, it arrives at the drafting frame. Since the roving before it reaches the twisting zone is more tightly defined by reason of the condensing or compaction steps, the twist tends to jump practically to the nip of the last roller pair in the path of the yarn before the spinning station and the so-called "spinning triangle" can be relatively small. Losses of edge fibers from the yarn can be minimal and the number of fibers which project out of the yarn can be small as well so that the finished yarn has a low degree of hairiness.